Active stream format for holding multiple media streams

ABSTRACT

An active stream format is defined and adopted for a logical structure that encapsulates multiple data streams. The data streams may be of different media. The data of the data streams is partitioned into packets that are suitable for transmission over a transport medium. The packets may include error correcting information. The packets may also include clock licenses for dictating the advancement of a clock when the data streams are rendered. The format of ASF facilitates flexibility and choice of packet size and in specifying maximum bit rate at which data may be rendered. Error concealment strategies may be employed in the packetization of data to distribute portions of samples to multiple packets. Property information may be replicated and stored in separate packets to enhance its error tolerance. The format facilitates dynamic definition of media types and the packetization of data in such dynamically defined data types within the format.

RELATED APPLICATIONS

The present application claim priority under 35 U.S.C. §120 as acontinuation of U.S. patent application Ser. No. 10/376,428, filed Feb.28, 2003, which is a divisional of U.S. patent application Ser. No.09/510,565, filed on Feb. 22, 2000, which is a divisional of U.S. patentapplication Ser. No. 08/813,151, filed on Mar. 7, 1997, now U.S. Pat.No. 6,041,345, which claims priority from Provisional Application Ser.No. 60/013,029, filed on Mar. 8, 1996, and which claims priority fromProvisional Application Ser. No. 60/028,789, filed on Oct. 21, 1996, allof which are incorporated herein in their entireties by reference.

TECHNICAL FIELD

The present invention relates generally to data processing systems andmore particularly to an active stream format for holding multiple mediastreams.

BACKGROUND OF THE INVENTION

Conventional file and/or stream formats for transmitting multiple datastreams of varying media are limited in several respects. First, theseformats are generally limited in the packet sizes that are available forencapsulating data. Such formats, if they specify packets, specify thepackets as a given fixed size. Another limitation of such formats isthat they do not facilitate the use of error correction codes. A furtherweakness of these conventional formats is that they do not provideflexibility in timing models for rendering the data encapsulated withinthe format. An additional limitation with such formats is that they arenot well adapted for different transport mediums that have differentlevels of reliability and different transmission capabilities.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, a computersystem has a logical structure for encapsulating multiple streams ofdata that are partitioned into packets for holding samples of data fromthe multiple data streams. A method of incorporating error correctioninto the logical structure is performed on the computer system. Inaccordance with this method, a portion of at least one packet isdesignated for holding error correcting data. The error correcting datais then stored in the designated portion of the packet.

In accordance with another aspect of the present invention, multiplestreams of data are stored in packets and error correcting data isstored in at least some of the packets. The packets are encapsulatedinto a larger stream and information regarding what error correctingmethods are employed for the packets is also stored in the packets.

In accordance with yet another aspect of the present invention, samplesof data from multiple data streams are stored in packets, and replicasof information are stored in at least some of the packets. A flag is setin each of the packets that holds replicas to indicate that the packetshold the replicas. The packets are encapsulated into a larger logicalstructure and transmitted to a destination.

In accordance with a further aspect of the present invention, a logicalstructure is provided for encapsulating multiple streams of data wherethe streams of data are stored in packets. Clock licenses that dictateadvancement of a clock are stored in multiple ones of the packets. Thelogical structure is transmitted from a source computer to a destinationcomputer. The clock is advanced at the destination computer as dictatedby the clock license for each packet that holds a clock license inresponse to the receipt or processing of the packet at the destinationcomputer.

In accordance with an additional aspect of the present invention, astream format is provided for encapsulating multiple streams of data.The stream format includes a field for specifying a packet size forholding samples of the multiple streams of data. In a logical structurethat adopts the stream format, a value is stored in the field thatcorresponds to the desired packet size. Packets of the desired size arestored within the logical structure and the logical structure istransmitted over a transport medium to the destination.

In accordance with a further aspect of the present invention, a streamformat is provided for encapsulating multiple streams of data. A fieldis included in a logical structure that adopts the stream format forholding a value that specifies a maximum bit rate at which the multiplestreams may be rendered at the destination. A value is stored in thefield and the logical structure is transmitted over a transport mediumto a destination.

In accordance with another aspect of the present invention, a streamformat is provided for encapsulating multiple data streams and a newmedia type is dynamically defined. An identifier of the media type isstored in a logical structure that adopts the stream format and packetsof the new media type are stored in the logical structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a computer system that issuitable for practicing the preferred embodiment of the presentinvention.

FIG. 2 is a flowchart illustrating use of the ASF stream in accordancewith a preferred embodiment of the present invention.

FIG. 3 is a block diagram illustrating the components of the ASF stream.

FIG. 4 is a block diagram illustrating the format of the header_object.

FIG. 5 is a block diagram illustrating the format of theproperties_object.

FIG. 6A is a flowchart illustrating the steps that are performed to fillin packet size fields within the ASF stream.

FIG. 6B is a diagram illustrating different packet sizes and respectiveASF streams.

FIG. 7 is a block diagram illustrating the format of thestream_properties_object.

FIG. 8 is a diagram that illustrates the partitioning of a sample forstorage in multiple packets.

FIG. 9 is a diagram that illustrates the format of thecontent_description_object.

FIG. 10A is a diagram illustrating the format of the marker_object.

FIG. 10B is a diagram illustrating the format of a marker entry.

FIG. 11 is a diagram illustrating the format of theerror_correction_object.

FIG. 12 is flowchart illustrating the steps that are performed toutilize error correcting information in accordance with a preferredembodiment of the present invention.

FIG. 13 is a diagram illustrating format of the clock_object.

FIG. 14A is a diagram illustrating the format of thescript_command_object.

FIG. 14B is a diagram illustrating the format of a type_names_struc.

FIG. 14C is a diagram illustrating the format of a command_entry.

FIG. 15A is a diagram illustrating the format of the codec_object.

FIG. 15B is a diagram of a CodecEntry.

FIG. 16 is a diagram illustrating the format of the data_object.

FIG. 17 illustrates the format of a packet.

FIG. 18A illustrates a first format that the initial_structure mayassume.

FIG. 18B illustrates a second format that the initial_structure mayassume.

FIG. 19 illustrates the format of a payload_struc.

FIG. 20 is a diagram illustrating the format of the index_object.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment of the present invention employs an activestream format (ASF) for holding multiple media streams. ASF is wellsuited for storage of multimedia streams as well as transmission ofmultiple media streams over a transport medium. ASF is constructed toencapsulate diverse multimedia streams and facilitates optimalinterleaving of respective media streams. ASF specifies thepacketization of data and provides flexibility in choosing packet sizes.In addition, ASF enables the specification of a maximum datatransmission rate. As such, the packetization and transmission of mediastreams may be tailored to facilitate the bandwidth limitations of thesystem on which media streams are stored or transmitted.

ASF facilitates the use of error correction and error concealmenttechniques on the media streams. In unreliable transport mediums, sucherror correction and error concealment is highly beneficial. ASF isindependent of media types and is extensible to handle newly definedmedia types. ASF supports flexible timing approaches and allows anauthor of an ASF stream to specify the synchronization of events. ASFsupports synchronized rendering using a variety of synchronization clocktypes and provides index information which can be used as markers forlookup to provide playback features such as fast forward and fastreverse.

FIG. 1 is a block diagram of an illustrative system for practicing thepreferred embodiment of the present invention. FIG. 2 is a flowchartthat illustrates the steps that are performed in the illustrativeembodiment of FIG. 1. An ASF stream 16 is built by an author (step 20 inFIG. 2) and stored on a storage 14 on a source computer 10. As will bedescribed in more detail below, ASF allows the author to design thestream for a most efficient storage based on the type of source computer10 on which it is stored. Sometime later, the ASF stream 16 istransferred over a transport media 17, such as a network connection, toa destination computer 12 (step 24 in FIG. 2). The destination computer12 includes a number of renderers 18 for rendering the media types thatare present within the ASF stream 16. For example, the ASF stream 16 mayinclude audio-type data and video-type data. The renderers 18 at thedestination 12 include an audio renderer and a video renderer. Therenderers may begin rendering data as soon as they receive data prior tothe complete transmission of the entire ASF stream 16 (see step 26 inFIG. 2). The renderers need not immediately render the data, but rathermay render the data at a later point in time.

FIG. 3 depicts the basic logical organization of an ASF stream 16. It isup to the author to fill in the contents of the ASF stream in accordancewith this format. The ASF stream 16 is divisible into a header section28, a data section 30 and an index section 49. In general, the headersection is first transmitted from the source computer 10 to thedestination computer 12 so that the destination computer may process theinformation within the header section. Subsequently, the data section 30is transmitted from the source computer 10 to the destination computer12 on a packet-by-packet basis and the index section 49 is transmitted.The header section 28 includes a number of objects that describe the ASFstream 16 in aggregate. The header section 28 includes a header_object32 that identifies the beginning of the ASF header section 28 andspecifies the number of objects contained within the header section.FIG. 4 depicts the format of the header_object 32 in more detail. Theheader_object 32 includes an object_id field 50 that holds a UUID forthe header_object. The UUID is an identifier. The header_object 32 alsoincludes a size field 52 that specifies a 64-bit quantity that describesthe size of the header section 28 in bytes. The header_object 32additionally includes a number_headers field 54 that holds a 32-bitnumber that specifies a count of the objects contained within the headersection that follow the header_object 32. An alignment field 55specifies packing alignment of objects within the header (e.g., bytealignment or word alignment). The architecture field 57 identifies thecomputer architecture type of the data section 30 at the index section49. The architecture field 57 specifies the architecture of thesesections as little endian or big endian.

The header_object 32 is followed in the header section 28 by aproperties_object 34, such as depicted in FIG. 5. The properties_object34 describes properties about the ASF stream 16. As can be seen in FIG.5, the properties_object 34 includes an object_id field 56 that holds aUUID and a size field 58 that specifies the size of theproperties_object 34. The properties_object 34 also includes amultimedia_stream_id field 60 that contains a UUID that identifies amultimedia ASF stream. A total_size field 62 is included in theproperties_object 34 to hold a 64-bit value that expresses the size ofthe entire ASF multimedia stream.

The properties_object 34 also holds a created field 64 that holds atimestamp that specifies when the ASF stream was created. A num_packetfield 65 holds a 64-bit value that defines the number of packets in thedata section 30. A play_duration field 66 holds a 32-bit number thatspecifies the play duration of the entire ASF stream in 100-nanosecondunits. For example, if the ASF stream 16 holds a movie, the durationfield 66 may hold the duration of the movie. The play_duration field 66is followed by a send_duration field 67 that corresponds to send the ASFstream in 100-nanosecond units. A preroll field 68 specifies the amountof time to buffer data before starting to play, and the flags field 70holds 32-bits of bit flags.

The properties object 34 includes a min_packet_size field 72 and amax_packet_size field 74. These fields 72 and 74 specify the size of thesmallest and largest packets 48 in the data section 30, respectively.These fields help to determine if the ASF stream 16 is playable fromservers that are constrained by packet size. For constant bit ratestreams, these values are set to have the same values. Amaximum_bit_rate field 76 holds a value that specifies the maximuminstantaneous bit rate (in bits per second) of the ASF stream.

FIG. 6A is a flowchart illustrating how these values are identified andassigned during authoring of the ASF stream 16. First, the size of thesmallest packet in the data section 30 is identified (step 78 in FIG.6A). The size of the smallest packet is stored in the min_packet_sizefield 72 (step 80 in FIG. 6A). The size of the largest packet in thedata section 30 is identified (step 82 in FIG. 6A), and the size isassigned to the max_packet_size field 74 (step 84 in FIG. 6A).

One of the beneficial features of ASF is its ability for facilitatingdifferent packet sizes for data of multiple media streams. FIG. 6B showsone example of two different streams 83 and 85. In stream 83, each ofthe packets is chosen to have a size of 512 bytes, whereas in stream 85each of the packets 48 holds 256 bytes. The decision as to the size ofthe packets may be influenced by the speed of the transport mechanismover which the ASF stream is to be transmitted, the protocol adopted bythe transport medium, and the reliability of the transport medium.

As mentioned above, the properties_object 34 holds a value in themaximum_bit_rate field 76 that specifies an instantaneous maximum bitrate in bits per second that is required to play the ASF stream 16. Theinclusion of this field 76 helps to identify the requirements necessaryto play the ASF stream 16.

The header section 28 (FIG. 3) must also include at least onestream_properties_object 36. The stream_properties_object 36 isassociated with a particular type of media stream that is encapsulatedwithin the ASF stream 16. For example, one of thestream_properties_objects 36 in the header section 28 may be associatedwith an audio stream, while another such object is associated with avideo stream. FIG. 7 depicts a format for such stream_properties_objects36. Each stream_properties_object 36 includes an object_id field 86 forholding a UUID for the object and a size field 88 for holding a valuethat specifies the size of the object in bytes. A stream_type field 90holds a value that identifies the media type of the associated stream.

The stream_properties_object 36 holds at least three fields 92, 98 and104 for holding information relating to error concealment strategies. Ingeneral, ASF facilitates the use of error concealment strategies thatseek to reduce the effect of losing information regarding a given sampleof media data. An example of an error concealment strategy is depictedin FIG. 8. A sample 106 is divided into four sections S.sub.1, S.sub.2,S.sub.3 and S.sub.4. When the sample is incorporated into packets in theASF stream, the samples are distributed into separate packets P.sub.1,P.sub.2, P.sub.3 and P.sub.4 so that if any of the packets are lost, theamount of data that is lost relative to the sample is not as great, andtechniques, such as interpolation, may be applied to conceal the error.Each sample has a number of associated properties that describe how bigthe sample is, how the sample should be presented to a viewer, and whatthe sample holds. Since the loss of the property information couldprevent the reconstruction of the sample, the properties information forthe entire sample is incorporated with the portions of the sample in thepackets.

The error_concealment_strategy field 92 holds a UUID that identifies theerror concealment strategy that is employed by the associated stream.The error_concealment_len field 98 describes the number of bytes in anerror concealment data block that is held in the error_concealment_dataentries 104. The properties associated with the error concealmentstrategy are placed in the error_concealment_data entries 104. Thenumber of entries will vary depending upon the error concealmentstrategy that is adopted.

The stream_properties_object 36 includes a stream_number field 100 thatholds an alias to a stream instance. The stream_properties_object 36also includes an offset field 94 that holds an offset value to thestream in milliseconds. This value is added to all of the timestamps ofthe samples in the associated stream to account for the offset of thestream with respect to the timeline of the program that renders thestream. Lastly, the stream_properties_object 36 holds atype_specific_len field 96 that holds a value that describes the numberof bytes in the type_specific_data entries 102. The type_specific_dataentries 102 hold properties values that are associated with the streamtype.

The header section 28 (FIG. 3) may also include a number of optionalobjects 38, 40, 42, 44, 45 and 46. These optional objects include acontent_description_object 38 that holds information such as the title,author, copyright information, and ratings information regarding the ASFstream. This information may be useful and necessary in instanceswherein the ASF stream 16 is a movie or other artistic work. Thecontent_description_object 38 includes an object_id field 110 and a sizefield 112 like the other objects in the header section 28. A title_lenfield 114 specifies the size in bytes of the title entries 119 that holdcharacter data for the title of the ASF stream 16. An author_len field115 specifies the size in bytes of the author entries 120 which hold thecharacters that specify the author of the ASF stream 16. Thecopyright_len field 116 holds the value that specifies the length inbytes of the copyright entries 121 that hold copyright informationregarding the ASF stream 16. The description_len field 117 holds a valuethat specifies the length in bytes of the description entries 122. Thedescription entries 122 hold a narrative description of the ASF stream16. Lastly, the rating_len field 118 specifies a size in bytes of therating entries 123 that hold rating information (e.g., X, R, PG-13) forthe ASF stream content.

The header section 28 may include a marker_object 40. The marker_object40 holds a pointer to a specific time within the data section 30. Themarker_object enables a user to quickly jump forward or backward tospecific data points (e.g., audio tracks) that are designated by markersheld within the marker_object 40.

FIG. 10A shows the marker_object 40 in more detail. The marker_object 40includes an object_id field 126 that holds a UUID, and a size field 128specifies the size of the marker_object in bytes. A marker_id field 130contains a UUID that identifies the marker data strategy, and anum_entries field 132 specifies the number of marker entries in themarker_object 40. An entry_alignment field 134 identifies the bytealignment of the marker data, and a name_len field 136 specifies howmany Unicode characters are held in the name field 138, which holds thename of the marker_object 40. Lastly, the marker_data field 140 holdsthe markers in a table. Each marker has an associated entry in thetable.

FIG. 10B shows the format of a marker entry 141 such as found in themarker_data field 140. An offset field 142 holds an offset in bytes fromthe start of packets in the data_object 47 indicating the position ofthe marker entry 141. A time field 144 specifies a time stamp for themarker entry 141. An entry_len field 146 specifies the size of anentry_data field 148, which is an array holding the data for the markerentry.

The header section 28 may also include an error_correction_object 42 foran error correction method that is employed in the ASF stream. Up tofour error correction methods may be defined for the ASF stream 16 and,thus, up to four error_correction_objects 42 may be stored within theheader section 28 of the ASF stream 16. FIG. 11 depicts the format ofthe error_correction_object 42.

The error_correction_object 42 includes an object_id field 150 and asize field 152, like those described above for the other objects in theheader section 28. The error_correction_object 42 also includes anerror_correction_id 154 that holds UUID that identifies the errorcorrecting methodology associated with the object 42. Theerror_correction_data_len field 156 specifies the length in bytes of theerror_correction_data entries 158 that hold octets for error correction.The error_correction_object 42 is used by the destination computer 12(FIG. 1) in playing the ASF stream 16.

FIG. 12 depicts a flowchart of how error correcting may be applied inthe preferred embodiment of the present invention. In particular, anerror correction methodology such as an N+1 parity scheme, is applied toone or more streams within the ASF stream 16 (step 160 in FIG. 12).Information regarding the error correcting methodology is then stored inthe error_correction_object 42 within the header section 28 (step 162 inFIG. 12). The source computer then accesses the error correctingmethodology information stored in the error_correction_object 42 inplaying back the ASF stream 16 (step 164 in FIG. 12). Error correctingdata is stored in the interleave_packets 48.

The header section 28 of the ASF stream 16 may also hold a clock_object44 that defines properties for the timeline for which events aresynchronized and against which multimedia objects are presented. FIG. 13depicts the format of the clock_object 44. An object_ID field 166 holdsa UUID to identify the object, and a size field 168 identifies the sizeof the clock_object 44 in bytes. A packet_clock_type field 170identifies the UUID of the clock_type that is used by the object. Apacket_clock_size field 172 identifies the clock size. Aclock_specific_len field 174 identifies the size and bytes of theclock_specific_data field 176 which contains clock-specific data. Theclock type alternatives include a clock that has a 32-bit source valueand a 16-bit duration value, a clock type that has a 64-bit source valueand a 32-bit duration value and a clock type that has a 64-bit sourcevalue and a 64-bit duration value.

The ASF stream 16 enables script commands to be embedded as a table inthe script_command_object 45. This object 45 may be found in the headersection 28 of the ASF stream 16. The script commands ride the ASF stream16 to the client where they are grabbed by event handlers and executed.FIG. 14A illustrates the format of the script_command_object 45. Likemany of the other objects in the header section 28, this object 45 mayinclude an object_ID field 178 for holding a UUID for the object and asize field 180 for holding the size in bytes of the object. A command_IDfield 182 identifies the structure of the command entry that is heldwithin the object.

The num_commands field 184 specifies the total number of script commandsthat are to be executed. The num_types field 186 specifies the totalnumber of different types of script_command types that have beenspecified. The type_names field 188 is an array of type_names_struc datastructures. FIG. 14B depicts the format of this data structure 192. Thetype_name_len field 194 specifies the number of Unicode characters inthe type_names field 196, which is a Unicode string array holding namesthat specify script command types.

The command_entry field 190 identifies what commands should be executedat which point in the timeline. The command_entry field 190 isimplemented as a table of script commands. Each command has anassociated command_entry element 198 as shown in FIG. 14C. Each suchelement 198 has a time field 200 that specifies when the script commandis to be executed and a type field 202 that is an index into thetype_names array 196 that identifies the start of a Unicode string forthe command type. A parameter field 204 holds a parameter value for thescript command type.

The script commands may be of a URL type that causes a client browser tobe executed to display an indicated URL. The script command may also beof a file name type that launches another ASF file to facilitate“continuous play” audio or video presentations. Those skilled in the artwill appreciate that other types of script commands may also be used.

The header section 28 of the ASF stream 16 may also include acodec_object 46. The codec_object 46 provides a mechanism to embedinformation about a codec dependency that is needed to render the datastream by that codec. The codec object includes a list of codec types(e.g., ACM or ICM) and a descriptive name which enables the constructionof a codec property page on the client. FIG. 15A depicts the format of acodec_object 46. The object_id field 206 holds a UUID for thecodec_object 46 and the size field 208 specifies the size of the object46 in bytes. The codec_ID field 210 holds a UUID that specifies thecodec_type used by the object. The codec_entry_len field 212 specifiesthe number of CodecEntry entries that are in the codec_entry field 214.The codec_entry field 214 contains codec-specific data and is an arrayof CodecEntry elements.

FIG. 15B depicts the format of a single CodecEntry element 216 as foundin the codec_entry field 214. A type field 218 specifies the type ofcodec. A name field 222 holds an array of Unicode characters thatspecifies the name of the codec and a name_len field 220 specifies thenumber of Unicode characters in the name field. The description field226 holds a description of the codec in Unicode characters and thedescription_len field 224 specifies the number of Unicode charactersheld within the description field. The cbinfo field 230 holds an arrayof octets that identify the type of the codec and the cbinfo_len field228 holds the number of bytes in the cbinfo field 230.

As mentioned above, the data section 30 follows the header section 28 inthe ASF stream 16. The data section includes a data_object 47 andinterleave_packets 48. A data_object 47 marks the beginning of the datasection 30 and correlates the header section 28 with the data section30. The packets 48 hold the data payloads for the media stream storedwithin the ASF stream 16.

FIG. 16 depicts the format of the data_object 46. Like other objects inthe ASF stream 16, data_object 46 includes an object_id field 232 and asize field 234. The data_object 46 also includes a multimedia_stream_idfield 236 that holds a UUID for the ASF stream 16. This value must matchthe value held in the multimedia_stream_id field 60 in theproperties_object 34 in the header section 28. The data_object 46 alsoincludes a num_packets field 238 that specifies the number ofinterleave_Packets 48 in the data section 30. An alignment field 240specifies the packing alignment within packets (e.g., byte alignment orword alignment), and the packet-alignment field 242 specifies the packetpacking alignment.

Each packet 48 has a format like that depicted in FIG. 17. Each packet48 begins with an initial_structure 244. The format of theinitial_structures 244 depends upon whether the first bit held withinthe structure is set or not. FIG. 18A depicts a first format of theinitial_structure 244 when the most significant bit is cleared (i.e.,has a value of zero). The most significant bit is theerror_correction_present flag 270 that specifies whether errorcorrection information is present within the initial_structure 244 ornot. In this case, because the bit 270 is cleared, there is no errorcorrection information contained within the initial_structure 244. Thisbit indicates whether or not error correction is used within the packet.The two bits that constitute the packet_len_type field 272 specify thesize of the packet_len field 256, which will be described in more detailbelow. The next two bits constitute the padding_len_type field 274 andspecify the length of the padding_len field 260, which will also bediscussed in more detail below. The next two bits constitute thesequence_type field 276 and specify the size of the sequence field 258.The final bit is the multiple_payloads_present flag 278 which specifieswhether or not multiple payloads are present within the packet. A valueof 1 indicates that multiple media stream samples (i.e., multiplepayloads) are present within the packet.

FIG. 18B depicts the format of the initial_structure 244 when theerror_correction_present bit is set (i.e., has a value of 1). In thisinstance, the first byte of the initial_structure 244 constitutes theec_flag field 280. The first bit within the ec_flag field is theerror_correction_present bit 270, which has been described above. Thetwo bits that follow the error_correction_present bit 270 constitute theerror_correction_len_type field 284 and specify the size of theerror_correction_data_len field 290. The next bit constitutes theopaque_data flag 286 which specifies whether opaque data exists or not.The final four bits constitute the error_correction_data length field288. If the error_correction_len_type field 284 has a value of “00” thenthe error_correction_data_length field 288 holds theerror_correction_data_len value and the error_correction_data_len field290 does not exist. Otherwise this field 288 has a value of “0000.” Whenthe error_correction_data_len field 290 is present, it specifies thenumber of bytes in the error_correction_data array 292. Theerror_correction_data array 292 holds an array of bytes that contain theactual per-packet data required to implement the selected errorcorrection method.

The initial_structure 244 may also include opaque data 300 if theopaque_data bit 286 is set. The initial structure includes a byte offlags 302. The most significant bit is a reserved bit 304 that is set toa value of “0.” The next two bits constitute the packet_len_type field306 that indicate the size of the packet_len field 256. The nextsubsequent two bits constitute the padding_len_type field 272 thatindicate the size of the padding_len field 274. These two bits arefollowed by another 2-bit field that constitutes the sequence_type offield 276 that specifies the size of the sequence field 258. The lastbit is the multiple_payloads_present bit 278 that specifies whether arenot multiple payloads are present.

The initial_structure 244 is followed by a stream_flag field 246 thatholds a byte consisting of four 2-bit fields. The first two bitsconstitute a stream_id_type field 248 that specifies the size of thestream_id field 314 within the payload_struc 266. The second mostsignificant bits constitute the object_id_type field 250 and indicatethe number of bits in the object_id field 316 of the payload_struc 266as either 0-bits, 8-bits, 16-bits or 32-bits. The third most significanttwo bits constitute the offset_type field 252, which specifies thelength of the offset field 318 within the payload_struc 266 as either0-bits, 8-bits, 16-bits or 32-bits. The least two significant bitsconstitute the replicated_data_type field 254 and these bits indicatethe number of bits that are present for the replicated_data_len field320 of the payload_struc 266.

The packet 48 also includes a packet_len field 256 that specifies thepacket length size. The sequence field 258 specifies the sequence numberfor the packet. The padding_len field 260 contains a number thatspecifies the number of padding bytes that are present at the end of thepacket to pad out the packet to a desirable size.

The packet 48 also contains a clock_data field 262 that contains datarepresenting time information. This data may include a clock licensethat contains a system clock reference that drives the progression ofthe time line under the timing model and a duration that specifies theeffective duration of the clock license. The duration field limits thevalidity of the license to a time specified in milliseconds. Under themodel adopted by the preferred embodiment of the present invention, thesource computer 10 issues a clock license to the destination computer 12that allows the clock of the destination computer 12 to progress forwardfor a period of time. The progression of time is gated by the arrival ofa new piece of data that contains a clock value with a valid clocklicense that is not expired.

The packet 48 also includes a payload-flag field 264 that specifies apayload length type and a designation of the number of payloads presentin the packet. The payload-flag field 264 is followed by one or morepayload_strucs 266. These structures contain payload information whichwill be described in more detail below. The final bits within the packet48 may constitute padding 268.

FIG. 19 depicts the payload_struc 266 in more detail. The stream_idfield 314 is an optional field that identifies the stream type of thepayload. The object_id field 316 may be included to hold an objectidentifier. An offset field 318 may be included to specify an offset ofthe payload within the ASF stream. The offset represents the startingaddress within a zero-address-based media stream sample where the packetpayload should be copied.

The payload_struc 266 may also include a replicated_data_len field 320that specifies the number of bytes of replicated data present in thereplicated_data field 322. As was discussed above, for protectionagainst possible errors, the packet 48 may include replicated data. Thisreplicated data is stored within the replicated_data field 322.

The payload_len field 323 specifies the number of payload bytes presentin the payload held within the payload_data field 325. The payload_datafield 326 holds an array of payloads (i.e., the data).

The ASF stream may also include an index_object 49 that holds indexinformation regarding the ASF stream 16. FIG. 20 depicts the format ofthe index_object 49. The index_object includes a number of indexentries. The index_object 49 includes an object_id field 324 and a sizefield 326. In addition, the index_object 49 includes an index_id field328 that holds a UUID for the index type. Multiple index_name_entriesmay be stored depending on the number of entries required to hold thecharacters of the name. For example, each entry may hold 16 charactersin an illustrative embodiment.

The index_object includes a time_delta field 330 that specifies a timeinterval between index entries. The time represents a point on thetimeline for the ASF stream 16. A max_packets field 332 specifies amaximum value for packet_count fields, which will be described in moredetail below. A num_entries field 334 is a 32-bit unsigned integer thatdescribes the maximum number of index entries that are defined withinthe index_info array 336. This array 336 is an array ofindex_information structures. Each index_info structure holds a packetfield that holds a packet number associated with the index entry and apacket_count field specifies the number of the packet to send with theindex entry so as to associate the index entries with the packets. InFIG. 21, the index_info array structure 336 holds N index_informationstructures and each index-information structure has a packet field338A-338N and a packet_count field 340A-340N.

While the present invention has been described with reference to apreferred embodiment thereof, those skilled in the art will appreciatethat various changes in form and detail may be made without departingfrom the intended scope of the invention as defined in the appendedclaims. For example, the present invention may be practiced with astream format that differs from the format described above. Theparticulars described above are intended merely to be illustrative. Thepresent invention may be practiced with stream formats that include onlya subset of the above-described fields or include additional fields thatdiffer from those described above. Moreover, the length of the valuesheld within the fields and the organization of the structures describedabove are not intended to limit the scope of the present invention.

1. A computer comprising: a processor; storage; and a logical structurestored in the storage encapsulating multiple data streams, data fromsaid data streams being incorporated in packets, wherein: the dataincorporated in the packets are of a new media type; the logicalstructure includes an identifier for the new media type; and theidentifier being used to determine a renderer to use to render data ofthe new media type; and a clock license being encapsulated into at leastone packet for advancing a clock at a destination when processed at thedestination the computer, utilizing the processor and storagefunctionality, transmit, the packets of the logical structure on apacket-by-packet basis over a network from the computer to a destinationcomputer.
 2. The computer of claim 1, wherein the logical structureholds a field for a maximum packet size and a field for a minimum packetsize.
 3. The computer of claim 1, wherein the multiple streams of datain the logical structure are Active Stream Format (ASF) data streams. 4.The computer of claim 1, wherein the logical structure holds a valuethat specifies a maximum bit rate at which the multiple streams of datamay be rendered.
 5. A system comprising: a processor; storagefunctionally coupled to the processor, wherein a logical structure isstored in the memory, the logic structure encapsulating multiple streamsof data, said streams of data being stored in packets, by: storingsamples of data from multiple data streams in the packets; storingreplicas of information in at least some of the packets; storing errorcorrecting data in the at least some of the packets, wherein the errorcorrecting data identifies an error correcting method for the at leastsome of the packets; setting a flag in the packets that hold thereplicas; storing in the logical structure a field for a maximum packetsize and a field for a minimum packet size; and encapsulating thepackets into the logical structure, wherein at least some of the packetshold the replicas; storing clock licenses that dictate advancement of aclock in multiple ones of the packets; the system, utilizing theprocessor and storage functionality, transmit, the packets of thelogical structure on a packet-by-packet basis over a network from thesource computer to the destination computer; and for each packet thatholds a clock license, advancing the clock at the destination computeras dictated by the clock license in response to receiving the packet atthe destination computer.
 6. The system as defined in claim 5, whereinthe replicas of information hold property information regarding thesamples of data.
 7. The system of claim 5 wherein portions of a sampleare stored in selected packets and a replica of property informationregarding the sample is stored in each packet in which a portion of thesample is stored.
 8. The system of claim 5, further comprising the stepof examining one of the replicas of information at the destinationcomputer when one of the packets is lost during the transmitting.
 9. Thesystem of claim 5, further comprising using the error correcting data inthe at least some of the packets to correct an error when thetransmitted logical structure is received at the destination.
 10. Thesystem as defined in claim 5, wherein the multiple streams of data inthe logical structure are Active Stream Format (ASF) data streams. 11.The system of claim 5, wherein: the logical structure includes a headersection and a data section; and the error correcting data is stored inmultiple packets in the data section.
 12. The system of claim 11,wherein information in the header section of the logical structureindicates what error correcting methodology is used with the errorcorrecting data stored in the multiple packets in the data section. 13.The system of claim 11, wherein the header section holds informationregarding multiple error correcting methods.
 14. The system of claim 11,wherein the error correcting data identifies one of a plurality of errorcorrecting methods.
 15. The system of claim 11, wherein the errorcorrecting data holds parity bits.
 16. A computer comprising: Aprocessor; storage; and a logical structure stored in the storageencapsulating multiple data streams, data from said data streams beingof a new media type and incorporated in packets, wherein the logicalstructure includes an identifier of the new media type from which arenderer can be determined to render the data of the new media type; anda clock license being encapsulated into at least one packet foradvancing a clock at a destination when processed at the destination,wherein: the streams of data stored in the packets are samples of datafrom multiple data streams in the packets for transmission on apacket-by-packet basis over a network; replicas of information arestored in at least some of the packets; error correcting data is storedin the at least some of the packets; the error correcting dataidentifies an error correcting method for the at least some of thepackets; and a flag is stored in each said packet that holds thereplicas; and the computer, utilizing the processor and storagefunctionality, transmit, the packets of the logical structure on apacket-by-packet basis over a network from the computer to a destinationcomputer.
 17. A computer comprising: a processor; storage; a logicalstructure stored in the storage encapsulating multiple data streams,wherein: the data from said data streams is incorporated in packets; andthe multiple streams of data in the logical structure are Active StreamFormat (ASF) data streams; a clock license being encapsulated into atleast one packet for advancing a clock at a destination when processedat the destination, wherein portions of a sample are stored in selectedpackets and a replica of property information regarding the sample isstored in each packet in which a portion of the sample is stored; andthe computer, utilizing the processor and storage functionality,transmit, the packets of the logical structure on a packet-by-packetbasis over a network from the computer to a destination computer. 18.The computer of claim 17, wherein: the logical structure includes aheader section and a data section, and the error correcting data isstored in multiple packets in the data section.
 19. The computer ofclaim 18, wherein information in the header section of the logicalstructure indicates what error correcting methodology is used with theerror correcting data stored in the multiple packets in the datasection.
 20. The data processing system as defined in claim 18, whereinthe header section holds information regarding multiple error correctingmethods.
 21. The computer of claim 18, wherein the error correcting dataidentifies a plurality of error correcting methods.
 22. The computer ofclaim 18, wherein the error correcting data holds parity bits.
 23. Thecomputer of claim 18, wherein the logical structure includes a field fora maximum packet size and a field for a minimum packet size.
 24. Thecomputer of claim 18, wherein the multiple streams of data in thelogical structure are Active Stream Format (ASF) data streams.
 25. Thecomputer of claim 18, wherein the logical structure includes a field forholding a value that specifies a maximum bit rate at which the multiplestreams of data may be rendered.
 26. The data processing system asdefined in claim 18, wherein the logical structure includes a field foran identifier of a new media type for the data from said data streamsincorporated in the packets and from which a renderer can be determinedto render the data of the new media type.